1. Field of the Invention
The present invention relates to a horn switch disposed on a steering wheel for a vehicle. More particularly, the invention relates to a horn switch that has two contact members and a support member, which is made of a light metallic material supporting one of the contact members, and that is enabled to operate a horn by bringing the contact members into contact with each other.
The present application is based on Japanese Patent Applications No. 2000-362356 and 2001-088703 and, which are incorporated herein by reference.
2. Description of the Related Art
As is known from Unexamined Japanese Publication No. Hei. 10-106382, a conventional horn switch of this kind is configured by comprising a stationary base portion, which supports a stationary contact member and is supported by a steering wheel body, and a movable base portion serving as a support member connected to a horn pad. The movable base portion is formed on a bag holder, on which an air bag device is disposed, and placed above the stationary base portion in such a way as to support the movable contact member that is enabled by being brought into contact with the stationary contact member to operate a horn. A forcing means for upwardly pushing the movable base portion is disposed between the movable base portion and the stationary base portion so that the movable contact member gets apart from the stationary contact member. The horn switch is constructed so that a pushing force of this forcing means pushes the movable contact member against the movable base portion. Further, usually, the bag holder having the movable base portion is formed from sheet plate.
Recently, it is desired from the viewpoint of reducing the weight of the air bug device that the bag holder be formed from a light metal, such as magnesium and aluminum. However, light metal is likely to be oxidized on the surface thereof. The movable contact member is constructed in such a way as to be press-contacted with the movable base portion only by a pushing force of the forcing means when the movable contact member formed from light metal is oxidized on the surface of a portion thereof near to the part thereof, which is in contact with the movable contact member. Thus, the contact state between the movable contact member and the movable member is liable to be poor. Consequently, it is difficult to ensure stable operability of the horn switch.
In view of the aforementioned drawbacks, an object of the invention is to provide a steering wheel horn switch enabled to ensure stable operability thereof even when a light metallic material is employed as the material thereof.
To achieve the foregoing object, according to the invention, there is provided a horn switch that is a steering wheel horn switch having two contact members enabled to operate a horn by being brought into contact with each other, and a support member, formed from a light metallic material, for supporting one of the contact members,
wherein a coil spring being disposed between the contact members and adapted to push the one of the contact members against the support member in such a way as to cause the one of the contact members to get apart from the other, and
wherein the one of the contact members and the support member being electrically conducted to each other in such a way as to be able to form a horn operating circuit. The steering wheel horn switch, characterized in that:
an electric conductor having electric conductivity, which is higher than that of the support member is disposed between the between the one of the contact members and the support member in such a manner as to come into contact with both of the other of the contact members and the support member, and
that the electric conductor is adapted to increase a contact area between the electric conductor and the support member so that the contact area therebetween is larger than a contact area between the other of the contact members and the support member in a case that the other of the contact member is singly brought into contact with the support member, or adapted to come into contact with the support member by being pushed by the other of the support member.
Further, in the case of an embodiment of this horn switch, it is preferable that the steering wheel has a steering wheel body and an air bag device,
that the air bag device has a bag holder formed from a light metallic material,
that the support member is constructed as a movable base portion disposed on the bag holder,
that the contact members include:
a stationary contact member supported on a top surface side of a stationary base portion placed at a side of the steering wheel body; and
a movable contact member supported on a bottom surface side of the movable base portion placed above the stationary base portion,
that the electric conductor is formed from a material, whose stiffness is higher than that of the support member, and placed between the movable contact member in such a way as to come in contact with both of the movable contact member and the movable base portion,
that a connection bolt is placed between the movable base portion and the stationary base portion in such a manner as to allow the movable base portion to downwardly move and as to restrict a separation distance from the stationary base portion to the movable base portion,
that the connection bolt has a head portion, which abuts against the bottom surface side of the stationary base portion, and a shank portion that upwardly extends from the head portion and is screwed into a screw hole formed in the movable base portion,
that the shank portion comprises a small-diameter male screw part, which is screwed into the screw hole formed in a tip end thereof, and a substantially cylindrical large-diameter part formed in the head portion,
that the movable contact member and the stationary contact member each have an insertion hole, through which the shank portion of the connection bolt is able to be inserted, and are substantially cylindrically shaped, and
that the male screw part is screwed into the screw hole so that the large-diameter part of the connection bolt abuts against the electric conductor.
Moreover, it is preferable that the electric conductor is constituted as a nut that is embedded in the movable base portion as an insert when the bag holder is formed by casting, and
that the nut has the screw hole, into which the male screw part of the connection bolt is able to be screwed, and is enabled to abut against the large-diameter part of the connection bolt.
Furthermore, it is preferable that the electric conductor is constituted as a plate disposed between the movable contact member and the movable base portion in such a way as to come in contact with both of the movable contact member and the movable base portion, and
that the plate is constructed in such a way as to have an insertion hole connected to the screw hole thereby to enable the male screw part to pass therethrough and as to be able to abut against the large-diameter part of the connection bolt.
Additionally, it is preferable that the plate is temporarily fixed to the connection bolt or the movable contact member.
According to the horn switch of the invention, the electric conductor, which is more resistant to oxidizing and has higher electric conductivity in comparison with the support member, intervenes between the one of the contact members and the support member in such a manner as to come into contact with both of this contact member and the support member. Thus, the contact member comes into contact with the electric conductor. Then, the support member and the electric conductor are brought into contact with each other. Therefore, even in the case where the horn switch is constructed so that the movable contact member is press-contacted with the electric conductor only by the pushing force of the coil spring, the electric conductor is reliably conducted from the contact member even when operated. Moreover, the electric conductor is in contact with the support member by increasing the contact area between the electric conductor and the support member in such a way as to be larger than the contact area between the support member and the one of the contact members, or by being pushed against the support member so that a conductive condition, in which the one of the contact members is electrically conducted to the support member, is better than the conductive condition in the case of allowing one of the contact members to singly come in contact with the support member. Thus, even when the surface of the support member is oxidized, the ability to electrically conduct the electric conductor to the support member is ensured. Consequently, the stable operability of the horn switch is ensured.
Further, according to the embodiment of the horn switch, even when the connection bolt is screwed to the movable base portion, the large-diameter part of the connection bolt is caused to abut against the electric conductor having stiffness, which is higher than that of the support member, instead of the support member that is formed from a light metallic material and liable to deform. Thus, the connection bolt is firmly screwed thereto, so that backlash or looseness is prevented from occurring when the connection bolt is screwed thereto. Consequently, a sufficient mounting strength of the horn switch is ensured.
Moreover, in the case where the electric conductor is constituted as a nut that is embedded in the movable base portion as an insert when the bag holder is formed by casting, and where the nut has the screw hole, into which the male screw part of the connection bolt is able to be screwed, and is enabled to abut against the large-diameter part of the connection bolt, the nut is embedded in the movable base portion. Thus, the surface of the movable base portion is resistant to oxidizing. Consequently, the contact between the nut and the movable base portion is stabilized. Moreover, higher ability to electrically conduct the contact member to the support member is ensured.
Furthermore, in the case where the electric conductor is constituted as a plate disposed between the movable contact member and the movable base portion in such a way as to come in contact with both of the movable contact member and the movable base portion, and where the plate is constructed in such a way as to have an insertion hole connected to the screw hole thereby to enable the male screw part to pass there through and as to be able to abut against the large-diameter part of the connection bolt, the connection bolt is screwed thereto, so that the plate is pushed against the movable base portion. Thus, the contact between the plate and the movable base portion is ensured. Further, sufficient conductivity is secured. Moreover, the manufacturing cost of the horn switch is reduced, as compared with that in the case that the nut is embedded in the movable base portion as an insert.
Besides, in the case where the horn switch is constructed so that the plate is temporarily fixed to the connection bolt or the movable contact member, the connection bolt is screwed into the screw hole in a state in which the plate is by preliminarily and temporarily assembling the plate to the connection bolt or the movable contact member, so that the plate is held by the connection bolt or the movable contact member.
Features and advantages of the invention will be evident from the following detailed description of the preferred embodiments described in conjunction with the attached drawings.